Many compounds with a chiral molecular structure that contain enantiomers are physiologically active and important as raw materials of drugs, agricultural chemicals, and food additives. In general, many enantiomers have completely different physiology activities from enantiomers of the same constituent elements in the same proportion by weight. For example, in the case of thalidomide, the R(−) enantiomer has a sedative effect and the S(−) enantiomer is teratogenic. For this reason, there has recently been an increasing demand for optical resolution of enantiomers, particularly in the pharmaceutical industry.
As the method for optical resolution of enantiomers, a preferential crystallization method in which one of the enantiomers is preferentially crystallized, a diastereomer method comprising causing a racemic isomer to react with another optically active substance to produce diastereomers and separating the resultant diastereomers by differences in crystallization properties, solubility in a solvent, and the like, a method of separating enantiomers by gas chromatography or high performance liquid chromatography using an adsorbent with a asymmetric structure as a stationary phase, a biochemical method of separating enantiomers utilizing the asymmetric discrimination capability of living bodies such as a digestive function and enzymatic, asymmetric hydrolysis, and the like.
Among these methods, the method of using chromatography is widely accepted due to the simple operation and the wide applicability to resolvable racemic isomers. Many types of adsorbents with an asymmetric structure used for the chromatography method are known, most of which are in the form of fine particles with a 10 μm or less particle size that can achieve a high theoretical plate number. This use of fine particles requires a significantly high operating pressure that may lead to deterioration of the separation performance during continuous operation for a long period of time as these adsorbents exhibit poor physical stability.
Published Japanese translation of PCT Application No. 2000-515627 discloses a chiral sorbent having a molded porous ceramic or a molded porous polyamide hollow fiber membrane as a substrate, in which the molded porous ceramic has macropores and mesopores, wherein the macropores are interconnected forming mesopores in the interconnected parts, the macropores have a median diameter greater than 0.1 μm, and the mesopores have a median diameter in the range of 2-100 nm. Enantiomers can be separated at a high flow rate by using these chiral sorbent in column chromatography.
Japanese Patent Application Laid-Open No. 2002-306976 discloses a porous ion exchange material having a continuous pore structure comprising macropores and mesopores (the macropores being interconnected forming mesopores with an average diameter of 1-1,000 μm in the interconnected parts), and having a total pore volume of 1-50 ml/g, uniformly distributed ion exchange groups, and an ion exchange capacity of 0.5 mg-equivalence/g or more on a dry basis. The pore volume and specific surface area of this organic porous ion exchange material are extremely large.
However, the chiral sorbent having a molded porous ceramic as a substrate disclosed in the Published Japanese translation of PCT Application No. 2000-515627 has a drawback of restrained separation conditions due to its unstable properties in alkalis, whereas the chiral sorbent having a molded porous polyamide hollow fiber membrane as a substrate allows only a small theoretical plate number, making it difficult to achieve precise separation. In addition, optical activity recognizing sites are introduced only to the surface, but can be introduced neither inside the skeletons of the inorganic molded porous ceramic material nor inside the polyamide hollow fiber membrane. These sorbents have, therefore, only a small adsorption capacity and are unsuitable for separation and purification of a large amount of enantiomers. The organic porous material having a continuous porous structure disclosed in the Japanese Patent Application Laid-Open No. 2002-306976, on the other hand, has been developed with an objective of using this material as an ion exchanger. There is no description in the patent specification regarding the use of this material as an adsorbent to separate enantiomers.
An object of the present invention is therefore to solve the above-mentioned shortcomings of the prior art. Specifically, an object of the present invention is to provide a non-particulate organic porous material possessing high physical stability, usable under wide separating conditions, and having a large adsorption capacity and to provide a method for manufacturing the same.